https://scholars.lib.ntu.edu.tw/handle/123456789/150243
標題: | 以序列式開關達成高密度與低界面阻抗的型電極陣列設計 Novel Design of High Density Microelectrode Arrayith Low Interfacial Impedance Using Serial Switches |
作者: | 楊豐旗 Yang, Feng-Chi |
關鍵字: | 微電極陣列;電極空間解析度;植入式電極;序列式開關;界面阻抗;Microelectrode Array;Spatial Resolution;Implantable Electrodes;Serial Switches;Interfacial Impedance | 公開日期: | 2008 | 摘要: | 在微電極相關應用研發上,如何增加電極分佈的空間解析度一直是個重要的問題。若以研究神經訊號傳遞網絡為其應用,則空間解析度應該要達到可對單一神經細胞定址,以期了解神經電生理訊號之走向路徑;若以電刺激為其應用,則需達精準的單或多點刺激,以避免對其他不必要部位的干擾;若做為人機介面,則可幫助解析訊號,增進訊號之判別以避免誤動作。由此可見空間解析度的需求與必要性。 就可穿刺性電極陣列技術發展而言,如何在提高空間解析度和縮小結構體的截面積以降低對組織的傷害,是設計上最重要的挑戰。為此本論文提出一種創新的高密度電極陣列設計方式,以一條輸出導線實現對所有電極(n個)的訊號傳輸功能,藉由犧牲一般電極即時量測的優點,在合理的時間解析度Δt下依序得到訊號。此模式的實現方法為將所有電極點(1~ n)藉由相對應的雙重類比開關(switch 1~ n)連接至同一條導線;由一控制電路,在T時間內依序開啟1至n的開關,以連接個別電極至輸出端,並以週期T重覆此步驟,以符合Nyquist取樣頻率之要求。在這種設計架構下,我們發現可以達到4.3倍一維微電極陣列的空間解析度,以避免增加穿刺結構的截面積。 論文中首先利用元件實現設計概念並進行參數量測與驗證以應用於後續之電路模擬。在實驗中,使用1kHz,25%工作週期的開關應用於四電極陣列量測,四個電極的輸入訊號依序為:40Hz、120Hz、無輸入及10kHz的0.5V正弦波,結果顯示整體電路工作模式符合當初設計之預期;進一步利用Hspice進行電路模擬以作為製作成積體電路的準備,以1kHz,25%工作週期的開關應用於四電極陣列量測,四個電極輸入訊號依序為:40Hz、120Hz、無輸入及10kHz的0.5V正弦波;模擬電路中所使用的MOS規格為:W=0.3(um),L=0.42(um)的pMOS和W=0.35(um),L=0.42(um)的nMOS),模擬結果也顯示相同的預期。最終以TSMC 1P6M 0.18um製程進行積體電路設計,在10(um) × 10(um)的面積內,完成一個電極所對應的開關及控制電路配置,並完成一維電極陣列之實作,單位密度達2.8(#/100um)。 針對電極界面阻抗與穩態訊號振幅之關係,發現開關結構的高頻動作有助於減低微電極之界面阻抗。實驗結果顯示,若於面積為(0.2mm)2的電極後接一個510Ω的匹配電阻(電極在1kHz下的阻抗約為585Ω,匹配電阻與阻抗比為0.87),並測量落於負載上的電壓,則在1MHz的開關作用下,訊號約增為三倍大;在模擬中,若於面積為(0.02mm)2的電極後接一個51kΩ的匹配電阻(電極在1kHz下的阻抗約為58.5kΩ,匹配電阻與阻抗比為0.87),並測量落於負載上的電壓,則在100kHz的開關作用下,訊號約增為六倍大。 For the application of microelectrode array (MEA), the spatial resolution of electrodes distribution is an important issue. When we are interested in the network of neural signal transmission, higher spatial resolution is need to address single neuron to understand the path of action potential. When electrodes are used for electrical stimulation, higher spatial resolution is prefered to achieve precise spatial operation for single or multiple sites. As a tool for human-machine interface, higher spatial resolution helps signal analysis and avoids mistaken actions. As far as the development of penetrable MEA is concerned, increasing spatial resolution and decreasing the cross section of shank to reduce tissue injury are both the most important challenges for design. To optimize these factors, a novel design of high resolution MEA is suggested as follows: only one wire is used for signal transmission of n electrodes. Instead of real time measurement, signals for all n electrodes are acquired in series under temporal resolution Δt using this design. The way to realize this design is that all n electrodes are connected to the same wire by corresponding n double bilateral switches. Using a control circuit, Switches are closed in series from 1 to n in T. And the individual electrode is connected to wire only when its corresponding switch is closed. The overall steps are repeated in T to achieve Nyquist Sampling theorem. Using this design, we can achieve 4.3 times spatial resolution to avoid increasing the cross section of shank. In this thesis, systems were set up by discrete components to test our design and then the circuit simulations were run on the basis of test results. In the test experiments, four-electrode arrays having switch structure were used for signal acquisition and switches were operated under 1kHz with 25% duty cycle. Three sinusoidal signals with the same amplitude (0.5V) and different frequency (40Hz, 120Hz and 10kHz) were measured by the four-electrode array. The results confirmed with the design. Based on the result of experiment, circuit simulation were run on Hspice for the preparation of IC fabrication. In the simulation, switches were operated under 1kHz with 25% duty cycle and Three sinusoidal signals with the same amplitude (0.5V) and different frequency (40Hz, 120Hz and 10kHz) were set as input signals. The pMOS used in the circuit had width of 0.3(um) and length of 0.42(um). The nMOS used in the circuit had width of 0.35(um) and length of 0.42(um). The simulation results also confirmed with the design. Finally, the corresponding switch and control circuit of one electrode were layout by TSMC 1P6M 0.18um process. The area of layout was 10(um)×10(um) and the density of electrode array could achieve 2.8(#/100um). From the relation between electrode interfacial impedance and signal amplitude of stable state, Interfacial impedance of microelectrode array is reduced when the corresponding switch is operated at high frequency. From the experimental result, a 510Ω matching resistor was used to connect with a electrode of (0.2mm)2, (the electrode interfacial impedance is 585Ω at 1kHz; the ratio of matching resistance to interfacial impedance is 0.87) and the voltage drop on the load was measured. The signal under 1MHz switch operation was three times larger the the signal without switch operation. From the experimental result, a 51kΩ matching resistor was used to connect with a electrode of (0.02mm)2, (the electrode interfacial impedance is 58.5Ω at 1kHz; the ratio of matching resistance to interfacial impedance is 0.87) and the voltage drop on the load was measured. The signal under 1MHz switch operation was six times larger the the signal without switch operation. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/187981 |
顯示於: | 電機工程學系 |
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ntu-97-R95921107-1.pdf | 23.32 kB | Adobe PDF | 檢視/開啟 |
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